Physiology Chapter 5: Skeletal Muscle Reflexes

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Questions and Answers

Which muscle sensory organ is primarily responsible for detecting muscle length?

Muscle spindle apparatus (correct)

Intrafusal fibers

Golgi tendon organs

Extrafusal fibers

What is the role of gamma motor neurons in muscle spindle function?

Initiate reflex responses

Control extrafusal fiber contraction

Detect muscle tension

Adjust spindle sensitivity (correct)

Which type of muscle fiber is associated with primary sensory nerve cells in the muscle spindle?

Type II sensory nerve fibers

Nuclear bag fibers (correct)

Nuclear chain fibers

Extrafusal fibers

What distinguishes muscles that require finer control, such as extraocular muscles, from others?

Greater number of muscle spindles Signup and view all the answers

What kind of reflex is primarily mediated by the muscle spindle apparatus?

Stretch reflex Signup and view all the answers

Which of the following best describes the role of Golgi tendon organs?

Respond to tension exerted on tendons Signup and view all the answers

During coactivation of alpha and gamma motor neurons, what occurs within the muscle spindle?

Both intra- and extrafusal fibers contract Signup and view all the answers

What type of feedback do local motor control systems primarily utilize to adjust movements?

Sensory information from muscles and joints Signup and view all the answers

What is the main type of afferent nerve cells found in the muscle spindle apparatus?

Type II afferent nerves Signup and view all the answers

Which of the following statements is true regarding skeletal muscles?

They can contract in response to reflexive stimuli. Signup and view all the answers

What is the primary function of alpha-gamma coactivation in muscle spindles?

To prevent slackening of the spindle and loss of sensory information Signup and view all the answers

What characterizes the firing pattern of Type Ia and Type II sensory endings during rapid muscle stretch?

Type Ia shows an increase in firing rate, Type II shows a modest increase Signup and view all the answers

Which reflex is described as monosynaptic, and what does it primarily maintain?

Stretch reflex; optimal resting length of skeletal muscles Signup and view all the answers

What sequence accurately describes the activation of the monosynaptic stretch reflex?

Stretch on spindle activates sensory neuron, which in turn activates motor neuron Signup and view all the answers

What is the role of Golgi tendon organs (GTOs) in muscle function?

They protect muscles from injury due to excessive tension Signup and view all the answers

What occurs during the process of disinhibition as it relates to GTOs?

Minimization of GTO influence to enhance performance Signup and view all the answers

Which of the following best describes the Golgi tendon reflex?

It reduces tension in the muscle by inhibiting the motor neuron through an interneuron Signup and view all the answers

What effect does a sudden, unaccustomed movement have on Golgi tendon organs?

They inhibit muscle contraction to prevent damage Signup and view all the answers

How does Type Ia sensory ending contribute to the perception of muscle stretch?

It provides information on both the velocity and the angle of stretch Signup and view all the answers

Which of the following statements about the knee-jerk reflex is true?

It is a classic example of a monosynaptic reflex Signup and view all the answers

Study Notes

Physiology of Skeletal Muscle Reflex Responses

Skeletal muscles are typically voluntary, controlled by higher brain regions.
They can also contract unconsciously in response to stimuli.
MD137: Principles of Physiology course covers skeletal muscle reflex responses, focusing on muscle spindle apparatus and Golgi tendon organs.
The course is taught by Dr. K.McCullagh.
The nervous system plays a crucial role in controlling movements.
See Chapter 5 in Medical Physiology (Rhoades & Bell, 4th Edition) for more detailed information on nervous system control of movement.

Classification of Muscle Types

Muscles are categorized by control mode (voluntary/involuntary), anatomic structure (skeletal, cardiac, visceral), and histological features (striated/smooth).
Involuntary reflexes are a subset of involuntary muscle activity.

Motor Control System

The motor control system includes several interconnected components, including the cerebral cortex, basal ganglia, thalamus, brainstem, cerebellum, and spinal cord.
α (alpha) motor neurons are the final common pathway, connecting the central nervous system to skeletal muscles.
Peripheral sensory input plays a vital role in motor control.

Local Control of Motor Neurons

Local control systems adjust motor neuron activity based on sensory information from muscles, tendons, and joints, to fine-tune movements.

Muscle Sensory Organs

Muscle spindle apparatus responds to muscle length.
Muscles with finer control have more spindles (e.g., extraocular muscles).
Stretching a muscle stretches the spindles.
Golgi tendon organs respond to tension on a tendon.

Muscle Spindle Apparatus

Contains intrafusal fibers, thin muscle cells.
Two types: nuclear bag fibers and nuclear chain fibers
Two types of sensory nerve cells (afferent nerves) surround the fibers:
- Primary (type Ia) on nuclear bag and nuclear chain fibers
- Secondary (type II) on nuclear chain fibers

Muscle Spindle (Mechanism of Action)

Diagrams show the function/structure of the muscle spindle apparatus.
Key diagrams display the workings of the muscle spindle during different types of contractions including: no alpha or gamma nerve, alpha nerve, and alpha and gamma nerve coactivation.
Alpha-gamma coactivation maintains spindle sensitivity during muscle contractions.
Type Ia endings report both velocity and length of muscle stretch.
Type II endings report muscle length.

Monosynaptic Stretch Reflex

The simplest reflex; only a sensory neuron synapses with a motor neuron in the spinal cord.
Maintains optimal resting length of skeletal muscles.
Can be stimulated by striking the patellar ligament (knee-jerk reflex).

Knee-Jerk Reflex

Sensory neuron activates an alpha motoneuron.
Spindle stretches, activating sensory neuron.
Alpha motoneuron stimulates extrafusal muscle fibers to contract.
Stretch on the spindle is reduced.
Striking the patellar ligament stretches the tendon, triggering the reflex.

Stretch Reflex (Protective Mechanism)

Stretch reflexes protect muscles from damage.
An added load stretches muscles, activating spindles that fire more.
Muscle contracts to restore position, preventing over-stretching.
Afferent sensory signals increase, resulting in spinal cord signals to muscles, increasing muscle activity.
The process involves negative feedback.

Golgi Tendon Organs (GTOs)

Constantly monitoring tension in tendons.
Sensory neurons stimulate interneurons in the spinal cord.
Interneurons inhibit motor neurons.
This reduces tendon tension.
A disynaptic reflex which involves two synapses.
GTOs protect muscles and surrounding tissue from injury due to sudden movement or excessive load during activities such as athletic training.
- Disinhibition is the process of minimizing GTO influence during training.

Flexor Withdrawal Reflex

Painful stimuli on skin activate flexor muscles and inhibit extensor muscles on the same side of the body.
This moves the affected limb away from the stimulus.
The same stimulus produces an opposing response on the opposite side of the body.
Reciprocal inhibition occurs, preventing conflict between muscles on different sides of the body.

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Description

Explore the physiology of skeletal muscle reflex responses in Chapter 5 of Medical Physiology, focusing on mechanisms such as the muscle spindle apparatus and Golgi tendon organs. This quiz delves into voluntary and involuntary muscle activity, as well as the role of the nervous system in motor control.